Known in the art is a two-stage process for desilication of aluminate liquors. In the first stage an aluminate liquor is treated in an autoclave to recover SiO.sub.2 in the form is alkaline aluminosilicates. In the second stage of desilication lime is introduced into the aluminate liquor, SiO.sub.2 is precipitated from the liquor in the form of calcium hydrogarnets of the formula: 3CaO.Al.sub.2 O.sub.3.mSiO.sub.2 (6-2m).H.sub.2 O, wherein m=0.1-0.2 (cf. Liner A.I. et al. "Alumina Production", Moscow, "Metallurgiya" Publishing House, 1978, p.252-254). However, the depth of desilication is insufficient, since it is still impossible to sufficiently fully remove the impurities of SiO.sub.2 and Fe.sub.2 O and produce a high-quality alumina.
Known in the art is a process, wherein lime is preliminarily mixed with the aluminate liquor and this mixture is used as a desilication agent (cf. USSR Inventor's Certificate No.325811). Though this process makes it possible to increase the degree of desilication, the content of impurities of SiO.sub.2 and Fe.sub.2 O.sub.3 in the aluminate liquor remains still high, wherefore quality of the thus-produced alumina does not correspond the high-purity grade.